LEWIS HAMILTON topped the timesheet after dominating practice in the afternoon session ahead of this weekend's Malaysian Grand Prix.

LEWIS HAMILTON remains unconvinced that he can challenge for pole at the Malaysian Grand Prix this weekend despite dominating both sessions of practice today.

The 25-year-old was fastest in the morning and afternoon around a sweltering Sepang circuit, clocking a best time of one minute 34.175 seconds.

Red Bull's Sebastian Vettel was just behind Hamilton in the second session and the German has claimed pole in the opening two races of the season, with only reliability issues preventing him from perhaps boasting a 100 per cent record so far.

Vettel reported concerns over a power steering problem before clocking his fastest lap today, while team-mate Mark Webber parked his car in the gravel less than 30 minutes in due to an engine problem to suggest Red Bull have not quite rectified their problems.

The Ferrari duo of Fernando Alonso and Felipe Massa finished seventh and 15th respectively, although they were on heavy fuel loads for the majority of the session.

But Hamilton believes it will still be difficult to challenge for a place at the front of the grid tomorrow.

"It has not been a bad day," he said. "It was probably the best feeling I have had in the car around this circuit. We have a good programme and we stuck to it. I am still trying to get an understanding of the tyres but generally it was a good feeling.

"I wouldn't say I was comfortable as I think our qualifying pace has not been great in the last two races. Hopefully tomorrow will be a little better for us but we have to look out for the weather.

"It appears we are quite competitive but we do not know what other people are doing for fuel etc; so we have to wait and see tomorrow."

Vettel was also cautious and felt he was a little off the pace.

"I wasn't 100 per cent happy today, I think we still need to get a little bit quicker," he said. "The McLarens and the Mercedes look quick and Ferrari have a decent long-run pace so we'll have to see where we are."

Nico Rosberg once again got the better of Mercedes team-mate Michael Schumacher with the duo third and fifth respectively, with McLaren's Jenson Button sandwiched in-between.

"We're steadily getting there and it's starting to take shape, which is encouraging," Button said. "We don't know what the weather's supposed to do tomorrow, but we'll deal with it whatever it is."

The Lotus pair of Jarno Trulli and Heikki Kovalainen were the quickest of this season's new teams as they took 18th and 19th place respectively.

Virgin Racing duo Timo Glock and Lucas di Grassi were 21st and 22nd but HRT will be happy to have enjoyed a trouble-free session for the first time this season.

Karun Chandhok was almost seven seconds off the pace in 23rd with team-mate Bruno Senna just behind in 24th, but they did not suffer a single mechanical problem.

"Technically everything worked well and this is very positive for the team to be running through a normal driving programme with a crew that worked very hard to make all of this happen," team principal Colin Kolles said.